Pebble heater design



May 216, i950 R. K. SIMMS PEBBLE HEATER DESIGN 2 Sheets-Sheet 1 Filed Dec. 5, 1947 INVENTOR. R K SIMMS Wm W FIG.

A T TORNEVS May 16, 1950 R. K. SIMMS PEBBLE HEATER DESIGN Filed Dec.

2 Sheets-Sheet 2 HOlVAE'TB INVENTOR.

' R.K.S|MMS BY 244m 3/ A 7'TORNEV5 ?atented May 16, 195

UNITED STATES PATENT FEEELE DESTGN Russell K. Sirnms, Bartlesville, 0mm, assighor' to Ih-lllips Petroleum Company, a corporation of Delaware Application December 5, 19 17, Serial No. 789,805

(Cl. Nil-55) 7 Claims. 1 a

This invention pertains to a process audappae ratus for effecting chemical reactions at elevated; temperatures. in the vapor phase. A specific aspe'ct. of the. invention relatesv to the conversionof hydrocarbons.

In various chemical processes the character of the reaction product is dependent upon the specific reaction time utilized, especially at elevated temperatures. In such processes performed in a reactor, either packed with a stationary contact bed or in which a moving contact bed continuously passes through the reaction chamber, there is a substantial vapor space above the contact mass in which the reactionpro-ducts are given: a. substantial soaking period which may result in undesirable side reactions between the vaporous constituents 'or iii decomposition of the. desired reaction product. For example, in the cracking of hydrocarbons for the production of menus, it is essentia to high yields of the olefin to remove the olefinrich cracked vapors from 'th' high temperature vapcr pace above the contact bed in the shortest possible time in order to avoid overcrackin with excessive deposition of "carbon on the wens of tnefv'apo'r space. l I

'In "the t pical pebble heater design, a pebble throat introduces hpt pe to the conversion chamber ata point a sub ntial distance below the upper end or the conversion chamber order to provide a gasc'ollectin s ace aboi/ethe pebble bed; In hydrocarbon cracking processes,- considerabl-e difileulty is experienced, not only in over-crackingof the feed: stool: this space abovethe pebblebed, but also in excessive depo sition of carbon around the .pebbl'e'throat. Factors contributing to the dif iculty are the extreme 1y high temperature of the throat through which the hottest pebbles are passing and eddy currents or stagnant areas in the vapor space where the. gases are subjected to: soaking and complete breakdown to carbon. In many hydrocarbon, cracking processes conducted in a pebble heater unit; the cracked, olefin-rich, gases, flowing from the pebble bedv to the product gas outlet are at a temperature of upwards of 1600 F. Due to the shape of the vapor space and the presence of the pebble inlet throat, eflluent vapors from the-pebble bed swirl around this area beforepassing through theoutlet, thus prolonging cracking time and reducing yield of olefin as well as, increasing carbon deposition. A-plurality ofoutlets improves the situation, but does not effect a.

complete solution to the problem. It is with the streamlining of the gas now through the free space above the contact mass in a conversion chamber and with the reduction in carbon use sition on the walls and throat of the reactor this space that this invention is concerned.

im ortant object "of the present invention is toprovide an improved reactor which reduces the residence time of the reaction: products the free space the reactor. Another object is to streamline the new of reaction products out or reaction. chamber. It is also an object at this inventionto eliminate stagnant areas: and eddy currents with concomitantreduction of car bon deposition the free space" above the "con tact mass in a reactor. Another object i's'tcrprotect the throat of a pebble heater reactor from excessive carbon deposition; Still another object is to increase the yield of the desired product certain hydrocarbon conversion re actions.- other objects of the invention will lie-- come apparentfrom the accompanying disclosure.

My invention-provides ror streamlining the new of gases through the tree space: above a contact mass or pebble bed in a reaction chamber byrestricting the 'cross 'secticnal area of the spacetn'reugh which the reactionproducts now by the use of names 'sh aped to direct the new into a plurality of outlets through the top of the: re= action chamber. By progressively reducing the effective cross sectidnal area of the: vapor space between the contact bed and the vapor outlets;

the flow rate of-the. gaseous product is increased proportionally, thereby reducing the residence reactor according to one embodiment of the invention.

Figure 2 a topplan view of the reactor with the right-half ofthe top closure member-removed. Figure 3' is a perspective viewof the reactor with the top closure member removed along; the

- line 3=3 of Figure l and with the shellrez-n'oved 5;; Referring now to the drawing, the reactor ismade up of an outer cylindrical shell I I enclosing a refractory lining I2 which may be made of conventional furnace refractories along with less expensive insulating materials and may consist of several layers with the more expensive refractory in the innermost layer. A top closure member I3 has the same construction as the cylindrical shell, being lined with refractory material I I and attached to the cylindrical shell by means of flanged members I4. Top closure member I3 is pierced by pebble inlet conduit I5 and a series of symmetrically arranged product outlet conduits IS. A refractory arched bafile II converges in cooperation with the walls of the reactor to form a funnel-shaped passageway to each of the product outlets. A ring member I8 suitably attached to pebble inlet conduit I5 near its lower end assists in supporting the baffles. represents a bed of pebbles or particulate contact material introduced through pebble inlet I5.

' Figure 2 shows an arrangement of four product outlets symmetrically arranged around an axially positioned pebble inlet. This figure shows supporting arches 2B for adjacent walls of arched funnels or baffles IT. The invention is not limited to the particular arrangement or number of product outlets or pebble inlets shown. It is feasible to use a plurality of pebble inlets along with a plurality of product outlets. Obviously, a symmetrical arrangement of the product outlets enhances the uniformity of gas flow and is advantageous although not absolutely necessary to the reactor design. The invention also encompasses an arrangement of two, three, and any reasonable number above four, product outlets arranged around the pebble inlet.

' Figure 3 offers a clearer picture of the funnelshaped baffles which serve to streamline and funnel the flow of product gas out of the reactor. The invention is not limited to the particular shape of baffles shown in the drawing although this is a preferred modification of the invention. Any curved and arched baffle which reduces the effective cross-sectional area across the free vapor space above the contact bed and streamlines and funnels the flow of product gas to the product gas outlets, resulting in more rapid removal of product gas from the vapor space above the contact bed, is within the scope of the invention.

5 Figure l shows a conventional arrangement of pebble heater apparatus including a pebble heating chamber 2| and a reaction chamber 22 connected by a pebble throat I5 which serves as a pebble inlet to the reactor. A pebble outlet 23 connects to a suitable elevator 24 by means of a chute 25. A chute 26 connects the delivery end of the elevator to a pebble inlet 2! entering heater 2I'. Hot combustion gas or a combustible mixture of air and fuel is admitted to heating chamber 2I through inlet 29 and combustion gas exhausts through stack 3| heating the pebbles to a desired temperature by direct contact therewith in passing through the chamber. Any desirable feed'is admitted to the reactor through line 32, passes upwardly through the hot pebble bed and exhausts through outlets I6. In pebble heater operation, a continuous mass of pebbles is circulated through the heater and reactor, absorbing heat in the heater and imparting heat to the feed gas in the reactor to heat up the reactants and furnish the heat of reaction required in the specific process being performed.

While it is preferable to use pebbles and pebble heater technique in the invention, any fluent mass of contact material can be used. The pebbles or contact material may be either catalytic or noncatalytic with respect to the particular process being performed. The term pebble as used in the art. designates a particulate, refractory, heat-transfer material of fluent form and size, but is usually substantially spherical and ranges in size from about inch to 1 inch.

Baiiles Il may be fabricated in a variety of ways. In many instances, it may be desirable to construct the reactor as shown in Figure l with flanged means for attaching the head or top closure member to the cylindrical side wall as shown in the figure. In numerous applications of the invention, the operating conditions will be such that the baffles can be advantageously constructed from alloy steels such as 25-20 chrome Numeral I9 I nickel steel. This is feasible where operating temperatures do not exceed about 2000 F. and where reactions involved are not deleteriously catalyzed by the metal. When the arched baffles are formed from such alloys, they may be hung or suspended from the dome of the reactor by conventional means and may be perfectly streamlined funnels, the upper end of which is attached directly to the outlet conduits by welding or flanging.

Under temperatures much above 2000 F. and where it is desirable to carry on the particular reaction or conversion without contact with a metal surface, the baflies may be constructed by forming them from an alloy steel with a refractory lining. In this case, the steel baflies are fabrigated with lugs or spines, or the equivalent thereof, on the inner surface. These projections from the inner surface serve as the attaching or retaining means for a refractory lining. Such a lining is conveniently formed from silimanite which comprises aluminum and silicon oxides. This material may be mixed with water and applied as a sort of plaster to the alloy as the inner surface of the baflle. Upon setting of the mix and proper heat treatment thereof, a refractory lining is produced. Other insulating and refractory materials may be applied in the same or other conventional manner. In some instances, it is desirable to apply a coating of cheaper insulating material to the baflle followed by a coating of more refractory material.

Another method of fabrication involves the use of super refractory brick or tile shapes. These bricks may be formed from conventional high temperature refractories such as those comprising aluminum oxide, magnesium oxide, thorium oxide, zirconium oxide, silicon carbide, etc., which are sold commercially under various trade names. In this type Of construction, it, is necessary to lay up or build the arched baffles into the refractory wall of the reactor. The baffles are not supported by suspension from the top of the reactor or the outlet conduits, but are supported at the base by the walls of the reactor. A supporting ring of skew blocks is built into the reactor lining in such a manner as to support the built up refractory baffles. In order to support the bottom edge of the baffles which terminate in the free space of the reactor, it is usually necessary to construct a refractory arch which is self-supporting and also capable of supporting the additional weight of the baffles or funnels. The outer edge of the arch is sprung from the skew blocks and the inner end wedges against the pebble throat or inlet. These sprung arches 20 in Figures 1 and 2, provide support under the lower adjacent edges of the baffles-asshown in the drawing.

- When the bafiles are built up from refractory tile shapes or bricks, it is usually not practical. to provide and lay tiles or bricks which will seal between the upper terminals of the bafiles and the reactor head or outlet conduits. It is usually more practical to use a flange on the reactor head and to insulate this head with castable or plastic refractory just prior. to placing it on the reactor. The plastic refractory thus seals around and against the refractory baffle. The reactor head may also be insulated by making a; template thereof which also incorporates the upper terminals of the funnel shaped bafiles making a negative of this template and casting the refractory head therefrom. An additional construction modification involves the use of wooden or light metal forms which are then filled with a refractory mix or a rammed refractory material. In this way, the funnel shaped bafiles are cast or formed in place and supported by skew blocks built into the reactor walls.

In some installations, it may be desirable to fill in with insulating material the void space blocked off by the baflle funnels I! and pebble inlet l5. In installations where heat loss is not an important factor, it may be advantageous to fabricate the reactor head or top closure member with ventilating holes or slots leading into the void space between the refractory funnels and the pebble throat or inlet. This type of construction will help to cool the throat wall and makes higher pebble temperatures possible with a given refractory material.

The foregoing example illustrates the utility of the invention in a specific application. A light paraflinic stream of the composition given taken from a fractionation plant is cracked in apparatus in accordance with the invention to produce an effluent of the composition set forth. The extremely short reaction time of .014 second is indicative of the manner in which the invention operates to effect high yield of olefins with relatively low conversion to hydrogen, methane, and heavier parafiins.

Numerous modifications of the invention may be made within the scope thereof which is limited only by the appended claims.

Iclaim:

1. A pebble heater reactor comprising in combination a substantially vertically disposed cylindrical walled chamber having a crowned top closure member, an axially disposed tubular inlet for pebbles extending a substantial distance through said. closure: member into the interior of said chamber, a plurality of; reaction product outlets symmetrically disposed around aforesaid inlet, bafile means for each of. said outlets extending from the proximity of the interior end. of aforesaid tubular inlet and in contact therewith upwardly andlaterally thereof to define an. essentially funnel-shaped zone communicating at its apexwith said outlet so as to streamline and funnel the flow of said reaction products through said zone without contacting said tubular inlet, inlet means in the lower portion of said reactor for introducing reactant gas, and outlet means in the lower portion of said reactor for withdrawing pebbles.

2. A pebble heater reactor comprising in combination a substantially vertically disposed cylindrical walled chamber having a crowned top closure member, an axially disposed tubular inlet for pebbles extending a substantial. distance through said closure member into the interior of said chamber, a plurality of spaced apart openings through said closure member for withdrawing reaction products from the reactor, a, plurality of essentially funnel-shaped chambers in communication at their apexes with said openings, said chambers being bounded by baflles extending from the proximity of the interior end of said tubular inlet curvilinearly upwardly and laterally to a juncture with the walls of said walled chamber so as to streamline and funnel the flow of said reaction products from said reactor, inlet means in the lower portion of said reactor for introducing reactant gas, and outlet means in the lower portion of said reactor for withdrawing pebbles.

3. The apparatus of claim 2 further characterized in that said bafiles substantially completely surround and shield the lateral surface of that portion of said tubular inlet extending into said reactor.

4. In a process for effecting thermal conversions in the vapor phase at elevated temperatures comprising introducing a suitable feed gas into the lower portion of a descending bed of hot contact material being introduced into a conversion zone through a contact material inlet protruding downwardly from the upper end of said conversion zone in such manner as to form a. substantial space between the upper surface of said bed and the upper end of said conversion zone, removing contact material from the lower portion of said conversion zone, and flowing conversion products from the upper end of said conversion zone; wherein desired conversion products suffer degradation upon continued residence time in said space; the improvement comprising funneling the flow of conversion products out of contact with said inlet through said space in a plurality of zones of progressively restricted cross-section in the direction of flow thereof, thereby decreasing the residence time of said conversion products in said space.

5. The process of claim 4 further characterized in that the feed gas comprises a hydrocarbon.

6. In a process for cracking hydrocarbons at elevated temperatures in the vapor phase comprising introducing a suitable hydrocarbon feed into the lower portion of a descending bed of hot contact material being introduced into a, cracking zone through a contact-material inlet means extending downwardly into said zone so as to form a substantial space between the upper surface of said bed and the upper end of said crackaaoaaaa lng zone, removing contact material from the lower portion of said cracking zone, and flowing reaction products from th upper end of the cracking zone; wherein desired products of the reaction suffer degradation upon continued residence time in said space with concomitant deposition of carbonaceous material on said inlet means; the improvement comprisin streamlining and tunneling the flow of reaction products out of contact with said inlet means upwardly through said space in a plurality of zones of progressively restricted cross-section in the direction of flow, thereby decreasing the residence time of said reaction products in said space and avoiding carbon deposition on said inlet means.

7. A reactor comprising in combination a vertical cylindrical shell having end closure members and a refractory lining enclosing a. reaction chamber; inlet means in the lower portion of said chamber for introducing gaseous reactant thereto; an axially disposed tubular pebble inlet extending downwardly into the upper section of said chamber so as to form a vapor collecting space in the upper end of said chamber when 8 pebbles are admitted thru said inlet; a plurality of symmetrically disposed openings in the top closure member for withdrawing gases from said chamber; a plurality of tapered refractory balfles each forming an upwardly converging gas 001- lecting zone communicating through its upper and smaller end with one of said openings, the lower and flared ends of said baflles occupying the inner horizontal cross-sectional area of said chamber exclusive of said pebble inlet in a symmetrical pattern around said pebble inlet; and 3 The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,436,780 Simpson Feb. 24, 1948 2,441,170 Rose et a1 May 11, 1948 

1. A PEBBLE HEATER REACTOR COMPRISING IN COMBINATION A SUBSTANTIALLY VERTICALLY DISPOSED CYLINDRICAL WALLED CHAMBER HAVING A CROWNED TOP CLOSURE MEMBER, AN AXIALLY DISPOSED TUBULAR INLET FOR PEBBLES EXTENDING A SUBSTANTIAL DISTANCES THROUGH SAID CLOSURE MEMBER INTO THE INTERIOR OF SAID CHAMBER, A PLURALITY OF REACTION PRODUCT OUTLETS SYMMETRICALLY DISPOSED AROUND AFORESAID INLET, BAFFLE MEANS FOR EACH OF SAID OUTLETS EXTENDING FROM THE PROXIMITY OF THE INTERIOR END OF AFORESAID TUBULAR INLET AND IN CONTACT THEREWITH UPWARDLY AND LATERALLY THEREOF TO DEFINE AN ESSENTIALLY FUNNEL-SHAPED ZONE COMMUNICATING AT ITS APEX WITH SAID OUTLET SO AS TO STREAMLINE AND FUNNEL THE FLOW OF SAID REACTION PRODUCTS THROUGH 